Ambient light cancellation circuit

ABSTRACT

An ambient light cancellation circuit functions as a K th -order filter to filter out an ambient light signal of the detection signal, wherein the K is not fewer than two. The circuit includes a capacitive transimpedance amplifying circuit including an amplifier, a capacitor circuit, and a switch circuit. The capacitor circuit includes one or more capacitive paths coupled in parallel. The switch circuit couples the amplifier with the capacitor circuit in a non-cross manner or a cross manner. The non-cross manner is applied N times to let the capacitor circuit sample the detection signal N times while the detection signal includes a controllable-light signal and the ambient light signal; and the cross manner is applied M times to let the capacitor circuit sample the inversion of the detection signal M times while the detection signal includes the ambient light signal without the controllable-light signal, wherein (N+M) equals (K+1).

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to an ambient light cancellation circuit,especially to an ambient light cancellation circuit functioning as aK^(th)-order filter for filtering out an ambient light signal.

2. Description of Related Art

A general photoplethysmography (PPG) device illuminates skin with acontrollable light source (e.g., a light emitting diode (LED)) anddetects the reflection light to measure the variation in opticalabsorption and thereby realize multiple kinds of applications (e.g., themeasurement of heartbeat and blood oxygen). However, in addition to thecontrollable light source, other light sources (e.g., sunlight andindoor light) usually exist in the same space, and the influence ofthese light sources (hereinafter referred to as “ambient light”) shouldbe eliminated to ensure the accuracy of the measurement of the variationin optical absorption. A hardware circuit can be used to cancel theambient light; however, using a hardware circuit functioning as amulti-order filter to cancel the ambient light is not found in theexisting ambient-light cancellation technologies.

SUMMARY OF THE INVENTION

An object of the present disclosure is to provide an ambient lightcancellation circuit functioning as a multi-order filter for cancellingan ambient light signal.

A first embodiment of the ambient light cancellation circuit of thepresent disclosure functions as a K^(th)-order filter to sample adetection signal (K+1) times during a sampling period and thereby filterout an ambient-light signal of the detection signal, wherein the K is aninteger greater than one and the detection signal is generated by aphotoelectric device. This embodiment includes a capacitivetransimpedance amplifying circuit including an amplifier, a capacitorcircuit, and a switch circuit. The amplifier includes an input node, aninverting input node, and an output node, wherein the input node is forreceiving a reference voltage and the inverting input node is forreceiving the detection signal. The capacitor circuit includes: a firstcapacitive path including a first capacitor which includes a firstelectrode and a second electrode. The switch circuit includes a firstswitch, a second switch, a third switch, and a fourth switch. The firstswitch is set between the first electrode and the inverting input node;the second switch is set between the second electrode and the outputnode; and the first switch and the second switch are scheduled to beturned on during N time slot(s) and to be turned off during M timeslot(s) so as to couple the first electrode with the inverting inputnode and couple the second electrode with the output node during the Ntime slot(s) and thereby allow the first capacitor to sample thedetection signal during the N time slot(s), wherein the N time slot(s)and the M time slot(s) are included in the sampling period, each of theN and the M is a positive integer, and the sum of the N and the M is notgreater than (K+1). The third switch is set between the second electrodeand the inverting input node; the fourth switch is set between the firstelectrode and the output node; and the third switch and the fourthswitch are scheduled to be turned on during the M time slot(s) and to beturned off during the N time slot(s) so as to couple the secondelectrode with the inverting input node and couple the first electrodewith the output node during the M time slot(s) and thereby allow thefirst capacitor to sample the inversion of the detection signal duringthe M time slot(s). The detection signal includes a controllable-lightsignal and the ambient-light signal during I time slot(s); the detectionsignal includes the ambient-light signal without including thecontrollable-light signal during J time slot(s); the I time slot(s)is/are the N time slot(s) or the M time slot(s). When the I time slot(s)is/are the N time slot(s), the J time slot(s) is/are the M time slot(s);and when the I time slot(s) is/are the M time slot(s), the J timeslot(s) is/are the N time slot(s).

In an exemplary implementation of the first embodiment, the capacitorcircuit includes a plurality of capacitive paths coupled in parallel.The plurality of capacitive paths include the aforementioned firstcapacitive path, and the conducting states of the multiple capacitivepaths and the capacitances of the multiple capacitive paths jointlydetermine a plurality of filter coefficients of the K^(th)-order filter.

A second embodiment of the ambient light cancellation circuit of thepresent disclosure functions as a K^(th)-order filter to sample adetection signal (K+1) times during a sampling period and thereby filterout an ambient-light signal of the detection signal, wherein the K is aninteger and the detection signal is generated by a photoelectric device.This embodiment includes a capacitive transimpedance amplifying circuitincluding an amplifier, a capacitor circuit, and a switch circuit. Theamplifier includes an input node, an inverting input node, and an outputnode, wherein the input node is for receiving a reference voltage andthe inverting input node is for receiving the detection signal. Thecapacitor circuit includes a first capacitive path and a secondcapacitive path. The first capacitive path includes a first capacitorwhich includes a first electrode and a second electrode; and the secondcapacitive path is coupled with the first capacitive path in parallel,and includes a second capacitive-path switch and a second capacitorwhich includes a third electrode and a fourth electrode, wherein one endof the second capacitive-path switch is coupled with the third electrodeand the other end of the second capacitive-path switch is coupled withthe first electrode. The switch circuit includes a first switch, asecond switch, a third switch, and a fourth switch. The first switch hasone end coupled with both of the first electrode and the secondcapacitive-path switch and has another end coupled with the invertinginput node; and the second switch has one end coupled with both of thesecond electrode and the fourth electrode and has another end coupledwith the output node, wherein the first switch and the second switch arescheduled to be turned on during N time slot(s) and to be turned offduring M time slot(s) so as to couple the first electrode with theinverting input node and couple the second electrode with the outputnode during the N time slot(s) and thereby allow the first capacitor tosample the detection signal during the N time slot(s), the N timeslot(s) and the M time slot(s) are included in the sampling period, eachof the N and the M is a positive integer, and the sum of the N and the Mis not greater than (K+1). The third switch has one end coupled withboth of the second electrode and the fourth electrode and has anotherend coupled with the inverting input node; and the fourth switch has oneend coupled with both of the first electrode and the secondcapacitive-path switch and has another end coupled with the output node,wherein the third switch and the fourth switch are scheduled to beturned on during the M time slot(s) and to be turned off during the Ntime slot(s) so as to couple the second electrode with the invertinginput node and couple the first electrode with the output node duringthe M time slot(s) and thereby allow the first capacitor to sample theinversion of the detection signal during the M time slot(s). In theabove embodiment, the second capacitive-path switch is only turned onduring X time slot(s) which as a whole is a part of the whole of the Ntime slot(s) and the M time slot(s), the X time slot(s) can be the Ntime slot(s) or be different from the N time slot(s), and the X is apositive integer. Furthermore, the detection signal includes acontrollable-light signal and the ambient-light signal during I timeslot(s); the detection signal includes the ambient-light signal withoutincluding the controllable-light signal during J time slot(s); the Itime slot(s) is/are the N time slot(s) or the M time slot(s); when the Itime slot(s) is/are the N time slot(s), the J time slot(s) is/are the Mtime slot(s); and when the I time slot(s) is/are the M time slot(s), theJ time slot(s) is/are the N time slot(s).

A modification to the second embodiment includes the following changes:the second capacitive-path switch is set at the other side of the secondcapacitor, and thus one end of the second capacitive-path switch iscoupled with the fourth electrode and the other end of the secondcapacitive-path switch is coupled with the second electrode.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiments that areillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of the ambient light cancellation circuit ofthe present disclosure.

FIG. 2 shows the capacitive transimpedance amplifying circuit of FIG. 1performing Z-domain sampling in time domain.

FIGS. 3 a ˜3 b jointly shows an exemplary implementation of the ambientlight cancellation circuit of the present disclosure.

FIGS. 4 a ˜4 c jointly shows an exemplary implementation of the ambientlight cancellation circuit of the present disclosure.

FIG. 5 shows another embodiment of the ambient light cancellationcircuit of the present disclosure.

FIG. 6 shows yet another embodiment of the ambient light cancellationcircuit of the present disclosure.

FIG. 7 shows yet another embodiment of the ambient light cancellationcircuit of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present specification discloses an ambient light cancellationcircuit functioning as a multi-order filter for filtering out an ambientlight signal. The ambient light cancellation circuit is applicable to aPhotoplethysmography (PPG) device, but the application of the presentinvention is not limited thereto.

FIG. 1 shows an embodiment of the ambient light cancellation circuit ofthe present disclosure. The ambient light cancellation circuit 100 ofFIG. 1 functions as a K^(th)-order filter to sample a detection signalS_(PD) (K+1) times during a sampling period and thereby filter out anambient-light signal of the detection signal S_(PD), wherein the K is apositive integer (e.g., an integer greater than one) and the detectionsignal S_(PD) is generated by a photoelectric device (e.g., a photodiode (PD)).

Referring to FIG. 1 , the ambient light cancellation circuit 100includes a capacitive transimpedance amplifying circuit 110. Thecapacitive transimpedance amplifying circuit 110 includes an amplifier112, a capacitor circuit 114, and a switch circuit 116. The details ofthese circuits are described in the following paragraphs.

Referring to FIG. 1 , the amplifier 112 includes an input node (i.e.,the symbol “+” of the amplifier 112), an inverting input node (i.e., thesymbol “−” of the amplifier 112), and an output node. The input node isfor receiving a reference voltage VREF and the inverting input node isfor receiving the detection signal S_(PD), wherein the reference voltageVREF can be determined according to the demand for implementation.

Referring to FIG. 1 , the capacitor circuit 114 includes a firstcapacitive path 1142. The first capacitive path 1142 includes a firstcapacitor C1. The first capacitor C1 includes a first electrode C1 ₁ anda second electrode C1 ₂.

Referring to FIG. 1 , the switch circuit 116 includes a first switchSW1(+), a second switch SW2(+), a third switch SW3(−), and a fourthswitch SW4(−). The first switch SW1(+) is set between the firstelectrode C1 ₁ and the inverting input node; the second switch SW2(+) isset between the second electrode C1 ₂ and the output node; the thirdswitch SW3(−) is set between the second electrode C1 ₂ and the invertinginput node; and the fourth switch SW4(−) is set between the firstelectrode C1 ₁ and the output node. The first switch SW1(+) and thesecond switch SW2(+) are scheduled to be turned on during N time slot(s)and to be turned off during M time slot(s) so as to couple the firstelectrode C1 ₁ with the inverting input node and couple the secondelectrode C1 ₂ with the output node during the N time slot(s) andthereby allow the first capacitor C1 to sample the detection signalS_(PD) during the N time slot(s). The N time slot(s) and the M timeslot(s) are included in the aforementioned sampling period, each of theN and the M is a positive integer, and the sum of the N and the M is notgreater than (K+1) (e.g., (N+M)=(K+1)). The third switch SW3(−) and thefourth switch SW4(−) are scheduled to be turned on during the M timeslot(s) and to be turned off during the N time slot(s) so as to couplethe second electrode C1 ₂ with the inverting input node and couple thefirst electrode C1 ₁ with the output node during the M time slot(s) andthereby allow the first capacitor C1 to sample the inversion of thedetection signal S_(PD) during the M time slot(s). It is noted that thedefinition of the detection signal S_(PD) and the definition of theinversion of the detection signal S_(PD) are corresponding definitions,and thus are interchangeable.

Referring to FIG. 1 , the detection signal S_(PD) includes acontrollable-light signal (e.g., a light signal originated from an LED)and the ambient-light signal during I time slot(s); the detection signalS_(PD) includes the ambient-light signal without including thecontrollable-light signal during J time slot(s); the I time slot(s) canbe the N time slot(s) or the M time slot(s). When the I time slot(s)is/are the N time slot(s), the J time slot(s) is/are the M time slot(s);and when the I time slot(s) is/are the M time slot(s), the J timeslot(s) is/are the N time slot(s). For example, the ambient lightcancellation circuit 100 is applied to a PPG device, thecontrollable-light signal is originated from at least one controllablelight source (e.g., at least one LED) of the PPG device, the at leastone controllable light source is turned on to emit light during the Ntime slot(s), and is turned off to stop emitting light during the M timeslot(s), and the ambient light signal varies with the variation in theintensity of the ambient light in the same space during the (N+M) timeslots; on the basis of the above: the switch circuit 116 couples theamplifier 112 with the capacitor circuit 114 in a non-cross mannerduring the N time slot(s) to allow the capacitor circuit 114 to samplethe detection signal S_(PD) and generate N mixed-light samplingresult(s); the switch circuit 116 couples the amplifier 112 with thecapacitor circuit 114 in a cross manner during the M time slot(s) toallow the capacitor circuit 114 to sample the inversion of the detectionsignal S_(PD) and generate M ambient-light sampling result(s); and the(N+M) sampling results are related with the variation in the chargesstored in the capacitor circuit 114 and can be learned from thevariation in the voltage at the output node of the amplifier 112. It isnoted that the control over the switch circuit 116 can be realized withknown/self-developed technologies. It is also noted that the controlover the switch circuit 116 is corresponding to the control over theaforementioned at least one controllable light source. The control overthe at least one controllable light source falls beyond the scope of thepresent disclosure.

Referring to FIG. 1 , the switch circuit 116 controls the couplingbetween the amplifier 112 and the capacitor circuit 114 to make thecapacitive transimpedance amplifying circuit 110 perform time domainsampling as in Z-domain (i.e., Z-transform) as shown in FIG. 2 andobtain the aforementioned N mixed-light sampling result(s) and the Mambient-light sampling result(s), wherein the Z-domain sampling and thetime domain are known in this technical field. Providing (M+N)=(K+1),the K^(th)-order filter (i.e., the ambient light cancellation circuit100) is characterized by the conversion equation “c₀z⁰+c₁z⁻¹+c₂z⁻²+ . .. +c_(K)z^(−K)”. Regarding the above equation, c₀˜c_(K) are filtercoefficients of the K^(th)-order filter and can be determined and/oradjusted according to the demand for implementation, and z⁰˜z^(−K) are(K+1) sampling results (i.e., the N mixed-light sampling result(s) andthe M ambient-light sampling result(s)) obtained in sampling timesequence (i.e., the sequence of T₀, T₁, T₂, T₃, . . . , and T_(K) inFIG. 2 ). For example, if (M+N)=(K+1) and N=M=2, the K^(th)-order filteris a third-order filter; when the (M+N) sampling results are “amixed-light sampling result obtained at T₀, an ambient-light samplingresult obtained at T₁, an ambient-light sampling result obtained at T₂,and a mixed-light sampling result obtained at T₃” in sequence, theconversion equation of the third-order filter can be expressed as“1z⁰−z¹−z⁻²+z⁻³”, which means the filtration result of the third-orderfilter is the sum of z⁰, −z⁻¹, −z⁻², and z⁻³. In the above example,after obtaining the four sampling results z⁰, −z⁻¹, −z⁻², and z⁻³, thethird-order filter outputs the sum of the sampling results (i.e., thesum of z⁰, −z⁻¹, −z⁻², and z⁻³) to a back-end circuit (e.g., ananalog-to-digital converter).

The filter coefficients c₀˜c_(K) of the conversion equation“c₀z⁰+c₁z⁻¹+c₂z⁻²+ . . . +c_(K)z^(−K)” can be determined and/ordynamically adjusted according to the demand for implementation. Forexample, as shown in FIGS. 3 a ˜3 b, the capacitor circuit 114 furtherincludes a second capacitive path 1144. The second capacitive path 1144is coupled with the first capacitive path 1142 in parallel, and includesa second capacitive-path switch SW_(C2) and a second capacitor C2. InFIGS. 3 a-3 b , the capacitance of the second capacitor C2 is equal tothe capacitance of the first capacitor C1, and each of the twocapacitances is

$\frac{C}{2};$

accordingly, the equivalent capacitance of the parallel-connectedcapacitors C1 and C2 is

${\frac{C}{2} + \frac{C}{2}} = {C.}$

Referring to FIG. 2 and FIG. 3 a , during the even time slots T₀ and T₂,the switch circuit 116 couples the amplifier 112 with the capacitor 114in a non-cross manner while the second capacitive-path switch SW_(C2) isturned on, and thus the first capacitive path 1142 and the secondcapacitive path 1144 sample the detection signal S_(PD) simultaneously(i.e., both the first capacitor C1 and the second capacitor C2 arecharged/discharged); providing the charge/discharge amount in a unit oftime ΔT is Q₁, the voltage difference between the inverting input nodeand the output node of the amplifier 112 is

$V_{1} = {\frac{Q_{1}}{C}.}$

Referring to FIG. 2 and FIG. 3 b , during the odd time slot T1, theswitch circuit 116 couples the amplifier 112 with the capacitor 114 in across manner while the second capacitive-path switch SW_(C2) is turnedoff, and thus the first capacitive path 1142 samples the inversion ofthe detection signal S_(PD) (i.e., only the first capacitor C1 isdischarged/charged); providing the discharge/charge amount in the unitof time ΔT is Q₂, the voltage difference between the inverting inputnode and the output node of the amplifier 112 is

${V_{2} = {{- \frac{Q_{2}}{\frac{C}{2}}} = {- \frac{2Q_{2}}{C}}}};$

as a result, if Q₂≈Q₁, V₂≈−2V₁. In light of the above, the ambient-lightcancellation 100 functions as a second-order filter and generates afiltration result “1z⁰−2z⁻¹+z⁻²” which can be scaled up/down with aknown/self-developed analog/digital manner. It is noted that the K is apositive integer in the example of FIGS. 3 a ˜′3 b.

The example of FIGS. 3 a ˜3 b can be modified as shown in FIGS. 4 a ˜4c. Referring to FIGS. 4 a ˜4 c, the capacitive path 114 includes jcapacitive paths from the 1^(st) capacitive path (which includes acapacitor n₁×C) to the j^(th) capacitive path (which includes acapacitor n₁×C), wherein each capacitive path includes a capacitor, thej^(th) capacitive path further includes a j^(th) capacitive-path switchSW_(Cj), each of n₁˜n_(j) is a scaling factor and can be determinedaccording to the demand for implementation, C denotes a unit ofcapacitance, and the j is an integer greater than two. FIGS. 4 a ˜4 cshow the sampling operation during three consecutive time slots (i.e.,the three consecutive time slots T₀, T₁, and T₂ in FIG. 2 ). Regardingthe example of FIGS. 4 a-4 c , the ambient-light cancellation circuit100 functions as a second-order filter and generates a filtration result

$z^{0} - {\frac{\sum\left( {n_{1},\ldots,n_{j}} \right)}{\sum\left( {n_{1},\ldots,n_{m}} \right)}z^{- 1}} + {\frac{\sum\left( {n_{1},\ldots,n_{j}} \right)}{\sum\left( {n_{1},\ldots,n_{k}} \right)}z^{- 2}}$

which can be scaled up/down with a known/self-developed analog/digitalmanner. Those having ordinary skill in the art can derive more examplesfrom the examples of FIGS. 3 a -4 c.

The embodiments of the present disclosure could be modified to includeat least one of the following features:

-   -   (1) Compared with the example of FIGS. 3 a ˜3 b, the second        capacitive-path switch SW_(C2) is set at the other side of the        second capacitor C2 as shown in FIG. 5 ; and compared with the        example of FIGS. 4 a ˜4 c, the j^(th) capacitive-path switch SW0        is set at the other side of the j^(th) capacitor n_(j)×C as        shown in FIG. 6 .    -   (2) Compared with the example of FIGS. 3 a ˜3 b, during the even        time slots T₀ and T₂ as shown in FIG. 2 , the switch circuit 116        couples the amplifier 112 with the capacitor circuit 114 in a        non-cross manner while the second capacitive-path switch SW_(C2)        is turned off; during the odd time slot T₁, the switch circuit        116 couples the amplifier 112 with the capacitor circuit 114 in        a cross manner while the second capacitive-path switch SW_(C2)        is turned on; and accordingly, the ambient light cancellation        circuit 100 generates a filtration result as follows:        2×(1z⁰−½z⁻¹+z⁻²).    -   (3) Referring to FIGS. 3 a ˜′3 b, when the switch circuit 116        couples the amplifier 112 with the capacitor circuit 114 in a        non-cross manner during a certain time slot, the second        capacitive-path switch SW_(C2) can optionally be turned on or        turned off, wherein the certain time slot is or is not one of        the aforementioned N time slot(s); and when the switch circuit        116 couples the amplifier 112 with the capacitor circuit 114 in        a cross manner during a certain time slot, the second        capacitive-path switch SW_(C2) can optionally be turned on or        turned off, wherein the certain time slot is or is not one of        the aforementioned M time slot(s).    -   (4) Referring to FIGS. 1 ˜4 c, any capacitor of the capacitor        circuit 114 is a capacitor of fixed capacitance or a capacitor        of adjustable capacitance. For example, the first capacitor C1        of the first capacitive path 1142 is an adjustable capacitor;        and when the capacitive transimpedance amplifying circuit 110        performs sampling during each time slot, the capacitance of the        adjustable capacitor can be determined according to the required        filtration result.    -   (5) When the N is greater than one, any two of the N time slots        are equal in time length (e.g., microseconds) or unequal in time        length; and when the M is greater than one, any two of the M        time slots are equal in time length (e.g., microseconds) or        unequal in time length.    -   (6) Any of the N time slot(s) is equal to any of the M time        slot(s) in time length (e.g., two microseconds).

The example of FIGS. 3 a ˜3 b can be modified as shown in FIG. 7 . Asshown in FIG. 7 , the capacitor circuit 114 includes a plurality ofcapacitive paths coupled in parallel. The plurality of capacitive pathsincludes the first capacitive path 1142. Each of the plurality ofcapacitive paths except the first capacitive path 1142 includes a switchand a capacitor, wherein the conducting state of the said switch (i.e.,the switch being turned on or turned off) and the capacitance of thesaid capacitor are determined according to the demand for implementationto determine the filter coefficient(s) of the K^(th)-order filter (i.e.,the ambient light cancellation circuit 100) and realize a requiredfiltration effect.

It is noted that people having ordinary skill in the art can selectivelyuse some or all of the features of any embodiment in this specificationor selectively use some or all of the features of multiple embodimentsin this specification to implement the present invention as long as suchimplementation is practicable; in other words, the way to implement thepresent invention is flexible based on the present disclosure.

To sum up, the ambient light cancellation circuit of the presentdisclosure functions as a multi-order filter to filter out anambient-light signal. Compared with the prior art, the ambient lightcancellation circuit of the present disclosure can be implementedflexibly to realize many kinds of filtration effects.

The aforementioned descriptions represent merely the preferredembodiments of the present invention, without any intention to limit thescope of the present invention thereto. Various equivalent changes,alterations, or modifications based on the claims of the presentinvention are all consequently viewed as being embraced by the scope ofthe present invention.

What is claimed is:
 1. An ambient light cancellation circuit functioningas a K^(th)-order filter for sampling a detection signal (K+1) timesduring a sampling period and thereby filtering out an ambient-lightsignal of the detection signal, wherein the K is an integer greater thanone, the detection signal is generated by a photoelectric device, andthe ambient light cancellation circuit comprises: a capacitivetransimpedance amplifying circuit including: an amplifier including aninput node, an inverting input node, and an output node, wherein theinput node is for receiving a reference voltage and the inverting inputnode is for receiving the detection signal; a capacitor circuitincluding: a first capacitive path including a first capacitor whichincludes a first electrode and a second electrode; and a switch circuitincluding: a first switch set between the first electrode and theinverting input node; a second switch set between the second electrodeand the output node, wherein the first switch and the second switch arescheduled to be turned on during N time slot(s) and to be turned offduring M time slot(s) so as to couple the first electrode with theinverting input node and couple the second electrode with the outputnode during the N time slot(s) and thereby allow the first capacitor tosample the detection signal during the N time slot(s), wherein the Ntime slot(s) and the M time slot(s) are included in the sampling period,each of the N and the M is a positive integer, and a sum of the N andthe M is not greater than (K+1); a third switch set between the secondelectrode and the inverting input node; and a fourth switch set betweenthe first electrode and the output node, wherein the third switch andthe fourth switch are scheduled to be turned on during the M timeslot(s) and to be turned off during the N time slot(s) so as to couplethe second electrode with the inverting input node and couple the firstelectrode with the output node during the M time slot(s) and therebyallow the first capacitor to sample an inversion of the detection signalduring the M time slot(s), wherein the detection signal includes acontrollable-light signal and the ambient-light signal during I timeslot(s); the detection signal includes the ambient-light signal withoutincluding the controllable-light signal during J time slot(s); the Itime slot(s) is/are the N time slot(s) or the M time slot(s); when the Itime slot(s) is/are the N time slot(s), the J time slot(s) is/are the Mtime slot(s); and when the I time slot(s) is/are the M time slot(s), theJ time slot(s) is/are the N time slot(s).
 2. The ambient lightcancellation circuit of claim 1, wherein the capacitor circuit furtherincludes: a second capacitive path coupled with the first capacitivepath in parallel, the second capacitive path including a secondcapacitive-path switch and a second capacitor which includes a thirdelectrode and a fourth electrode, one end of the second capacitive-pathswitch is coupled with the third electrode and another end of the secondcapacitive-path switch is coupled with the first electrode and theswitch circuit, wherein the third electrode is coupled with theinverting input node through the second capacitive-path switch and thefirst switch, and is coupled with the output node through the secondcapacitive-path switch and the fourth switch; the fourth electrode iscoupled with the output node through the second switch, and is coupledwith the inverting input node through the third switch; and the secondcapacitive-path switch is scheduled to be turned on only during the Ntime slot(s) or the M time slot(s).
 3. The ambient light cancellationcircuit of claim 2, wherein a capacitance of the first capacitor and acapacitance of the second capacitor jointly determine a plurality offilter coefficients of the K^(th)-order filter.
 4. The ambient lightcancellation circuit of claim 1, wherein the capacitor circuit furtherincludes: a second capacitive path coupled with the first capacitivepath in parallel, the second capacitive path including a secondcapacitive-path switch and a second capacitor which includes a thirdelectrode and a fourth electrode, one end of the second capacitive-pathswitch is coupled with the fourth electrode and another end of thesecond capacitive-path switch is coupled with the second electrode andthe switch circuit, wherein the third electrode is coupled with theinverting input node through the first switch, and is coupled with theoutput node through the fourth switch; the fourth electrode is coupledwith the output node through the second capacitive-path switch and thesecond switch, and is coupled with the inverting input node through thesecond capacitive-path switch and the third switch; and the secondcapacitive-path switch is scheduled to be turned on only during the Ntime slot(s) or the M time slot(s).
 5. The ambient light cancellationcircuit of claim 4, wherein a capacitance of the first capacitor and acapacitance of the second capacitor jointly determine a plurality offilter coefficients of the K^(th)-order filter.
 6. The ambient lightcancellation circuit of claim 1, wherein the capacitor circuit furtherincludes: a second capacitive path coupled with the first capacitivepath in parallel, the second capacitive path including a secondcapacitive-path switch and a second capacitor which includes a thirdelectrode and a fourth electrode, one end of the second capacitive-pathswitch is coupled with the third electrode and another end of the secondcapacitive-path switch is coupled with the first electrode and theswitch circuit, wherein the third electrode is coupled with theinverting input node through the second capacitive-path switch and thefirst switch, and is coupled with the output node through the secondcapacitive-path switch and the fourth switch; the fourth electrode iscoupled with the output node through the second switch, and is coupledwith the inverting input node through the third switch; and the secondcapacitive-path switch is scheduled to be turned on during X timeslot(s) and turned off during Y time slot(s), the X time slot(s) and theY time slot(s) are included in the sampling period, the X time slot(s)as a whole is different from the N time slot(s) and different from the Mtime slot(s), the Y time slot(s) as a whole is different from the N timeslot(s) and different from the M time slot(s), and each of the X and theY is an integer equal to or greater than zero.
 7. The ambient lightcancellation circuit of claim 6, wherein a capacitance of the firstcapacitor and a capacitance of the second capacitor jointly determine aplurality of filter coefficients of the K^(th)-order filter.
 8. Theambient light cancellation circuit of claim 1, wherein the capacitorcircuit further includes: a second capacitive path coupled with thefirst capacitive path in parallel, the second capacitive path includinga second capacitive-path switch and a second capacitor which includes athird electrode and a fourth electrode, one end of the secondcapacitive-path switch is coupled with the fourth electrode and anotherend of the second capacitive-path switch is coupled with the secondelectrode and the switch circuit, wherein the third electrode is coupledwith the inverting input node through the first switch, and is coupledwith the output node through the fourth switch; the fourth electrode iscoupled with the output node through the second capacitive-path switchand the second switch, and is coupled with the inverting input nodethrough the second capacitive-path switch and the third switch; and thesecond capacitive-path switch is scheduled to be turned on during X timeslot(s) and turned off during Y time slot(s), the X time slot(s) and theY time slot(s) are included in the sampling period, the X time slot(s)as a whole is different from the N time slot(s) and different from the Mtime slot(s), the Y time slot(s) as a whole is different from the N timeslot(s) and different from the M time slot(s), and each of the X and theY is an integer equal to or greater than zero.
 9. The ambient lightcancellation circuit of claim 8, wherein a capacitance of the firstcapacitor and a capacitance of the second capacitor jointly determine aplurality of filter coefficients of the K^(th)-order filter.
 10. Theambient light cancellation circuit of claim 1, wherein the capacitorcircuit includes multiple capacitive paths coupled in parallel, themultiple capacitive paths include the first capacitive path, andconducting states of the multiple capacitive paths and capacitances ofthe multiple capacitive paths jointly determine a plurality of filtercoefficients of the K^(th)-order filter.
 11. The ambient lightcancellation circuit of claim 10, wherein the sampling period includesat least (K+1) time slots in sequence; the at least (K+1) time slotsinclude an I^(th) time slot; P capacitive path(s) of the multiplecapacitive paths is/are scheduled to be turned on during the I^(th) timeslot to sample the detection signal or the inversion of the detectionsignal; an equivalent capacitance of the P capacitive path(s) determinesan I^(th) filter coefficient of the K^(th)-order filter; the I is apositive integer between one and (K+1); and the P is a positive integer.12. The ambient light cancellation circuit of claim 10, whereincapacitances of at least two of the multiple capacitive paths are equal.13. The ambient light cancellation circuit of claim 10, whereincapacitances of at least two of the multiple capacitive paths areunequal.
 14. The ambient light cancellation circuit of claim 10, whereinat least one of the multiple capacitive paths includes an adjustablecapacitor.
 15. The ambient light cancellation circuit of claim 1,wherein the first capacitor is an adjustable capacitor.
 16. The ambientlight cancellation circuit of claim 1, wherein each of the N and the Mis greater than one; any two of the N time slots are equal in timelength; and any two of the M time slots are equal in time length. 17.The ambient light cancellation circuit of claim 16, wherein any of the Ntime slots and any of the M time slots are equal in time length.
 18. Anambient light cancellation circuit functioning as a K^(th)-order filterfor sampling a detection signal (K+1) times during a sampling period andthereby filtering out an ambient-light signal of the detection signal,wherein the K is an integer, the detection signal is generated by aphotoelectric device, and the ambient light cancellation circuitcomprises: a capacitive transimpedance amplifying circuit including: anamplifier including an input node, an inverting input node, and anoutput node, wherein the input node is for receiving a reference voltageand the inverting input node is for receiving the detection signal; acapacitor circuit including: a first capacitive path including a firstcapacitor which includes a first electrode and a second electrode; and asecond capacitive path coupled with the first capacitive path inparallel, the second capacitive path including a second capacitive-pathswitch and a second capacitor which includes a third electrode and afourth electrode, wherein one end of the second capacitive-path switchis coupled with the third electrode and another end of the secondcapacitive-path switch is coupled with the first electrode; and a switchcircuit including: a first switch having one end coupled with both ofthe first electrode and the second capacitive-path switch and havinganother end coupled with the inverting input node; a second switchhaving one end coupled with both of the second electrode and the fourthelectrode and having another end coupled with the output node, whereinthe first switch and the second switch are scheduled to be turned onduring N time slot(s) and to be turned off during M time slot(s) so asto couple the first electrode with the inverting input node and couplethe second electrode with the output node during the N time slot(s) andthereby allow the first capacitor to sample the detection signal duringthe N time slot(s), wherein the N time slot(s) and the M time slot(s)are included in the sampling period, each of the N and the M is apositive integer, and a sum of the N and the M is not greater than(K+1); a third switch having one end coupled with both of the secondelectrode and the fourth electrode and having another end coupled withthe inverting input node; and a fourth switch having one end coupledwith both of the first electrode and the second capacitive-path switchand having another end coupled with the output node, wherein the thirdswitch and the fourth switch are scheduled to be turned on during the Mtime slot(s) and to be turned off during the N time slot(s) so as tocouple the second electrode with the inverting input node and couple thefirst electrode with the output node during the M time slot(s) andthereby allow the first capacitor to sample an inversion of thedetection signal during the M time slot(s), wherein the secondcapacitive-path switch is only turned on during X time slot(s) which isa part of a whole of the N time slot(s) and the M time slot(s), the Xtime slot(s) is the N time slot(s) or is different from the N timeslot(s), and the X is a positive integer; the detection signal includesa controllable-light signal and the ambient-light signal during I timeslot(s); the detection signal includes the ambient-light signal withoutincluding the controllable-light signal during J time slot(s); the Itime slot(s) is/are the N time slot(s) or the M time slot(s); when the Itime slot(s) is/are the N time slot(s), the J time slot(s) is/are the Mtime slot(s); and when the I time slot(s) is/are the M time slot(s), theJ time slot(s) is/are the N time slot(s).
 19. An ambient lightcancellation circuit functioning as a K^(th)-order filter for sampling adetection signal (K+1) times during a sampling period and therebyfiltering out an ambient-light signal of the detection signal, whereinthe K is an integer, the detection signal is generated by aphotoelectric device, and the ambient light cancellation circuitcomprises: a capacitive transimpedance amplifying circuit including: anamplifier including an input node, an inverting input node, and anoutput node, wherein the input node is for receiving a reference voltageand the inverting input node is for receiving the detection signal; acapacitor circuit including: a first capacitive path including a firstcapacitor which includes a first electrode and a second electrode; and asecond capacitive path coupled with the first capacitive path inparallel, the second capacitive path including a second capacitive-pathswitch and a second capacitor which includes a third electrode and afourth electrode, wherein one end of the second capacitive-path switchis coupled with the fourth electrode and another end of the secondcapacitive-path switch is coupled with the second electrode; and aswitch circuit including: a first switch having one end coupled withboth of the first electrode and the third electrode and having anotherend coupled with the inverting input node; a second switch having oneend coupled with both of the second electrode and the secondcapacitive-path switch and having another end coupled with the outputnode, wherein the first switch and the second switch are scheduled to beturned on during N time slot(s) and to be turned off during M timeslot(s) so as to couple the first electrode with the inverting inputnode and couple the second electrode with the output node during the Ntime slot(s) and thereby allow the first capacitor to sample thedetection signal during the N time slot(s), wherein the N time slot(s)and the M time slot(s) are included in the sampling period, each of theN and the M is a positive integer, and a sum of the N and the M is notgreater than (K+1); a third switch having one end coupled with both ofthe second electrode and the second capacitive-path switch and havinganother end coupled with the inverting input node; and a fourth switchhaving one end coupled with both of the first electrode and the thirdelectrode and having another end coupled with the output node, whereinthe third switch and the fourth switch are scheduled to be turned onduring the M time slot(s) and to be turned off during the N time slot(s)so as to couple the second electrode with the inverting input node andcouple the first electrode with the output node during the M timeslot(s) and thereby allow the first capacitor to sample an inversion ofthe detection signal during the M time slot(s), wherein the secondcapacitive-path switch is only turned on during X time slot(s) which isa part of a whole of the N time slot(s) and the M time slot(s), the Xtime slot(s) is the N time slot(s) or is different from the N timeslot(s), and the X is a positive integer; the detection signal includesa controllable-light signal and the ambient-light signal during I timeslot(s); the detection signal includes the ambient-light signal withoutincluding the controllable-light signal during J time slot(s); the Itime slot(s) is/are the N time slot(s) or the M time slot(s); when the Itime slot(s) is/are the N time slot(s), the J time slot(s) is/are the Mtime slot(s); and when the I time slot(s) is/are the M time slot(s), theJ time slot(s) is/are the N time slot(s).